In prior art, many different systems for motion control have been proposed and placed into commercial use. The evolution of motion control schemes has progressed, shifting from one paradigm to another over the past few decades. Performance, reliability and cost have been the main driving factor to affect such change. Characterization for these varying systems can be placed into three categories.
The first and the oldest paradigm proposed by prior art is the centralized motion control scheme shown in (FIG. 1). This implementation shows a distinct star topology where a central unit; also known as master controller in the context of motion control systems, is connected to a plurality of remote slave units which shall be termed axes or drives for the purpose of this context. The master controller will have visibility over the axes in terms of both position and velocity, thereby allowing for synchronization between all axes connected to the master controller. As a result, this particular implementation will maintain good control of motor and system characteristics. This is the typical method of choice for systems demanding high performance, particularly in scenarios requiring tight coordination between a plurality of moving axes. However such a system tends to be inflexible as all the system signals (feedbacks, amplifiers commands, inputs/outputs) need to be directly connected to the centralized motion controller. This presents a difficulty in terms of installation, maintenance and essentially reliability of the whole system.
Further still it should be noted that in the system discussed in prior art, the current control mechanism is a task performed by the remote slave units which consequentially results in tight coupling between the master controller and its remote slave units with respect to the overall control mechanism of the system. More specifically, that the position and velocity of each drive is digitally controlled and actuated by the master controller, with current control being typically realized by analog circuitry in the remote slave unit. This infers that from the perspective of the master controller, the current exerted on the motor (which is the direct element by which exerts force to move the motors) is not observable and therefore not controllable, and the final control is fully dependant on the remote slave units which results in a very rigid imposition on the proposed system.
Another form of centralized control methodology is via pulse and direction proposed by prior art, where the motion controller is essentially just a vehicle for calculating trajectories and communicating with each drive via pulse and direction commands. This topology is realized by having intelligent slave drives which have the capability to perform complex operation such as being able to perform position, velocity and current loop control by itself.
Implementations for this type of system are easy to install and flexible in terms of physical cabling which results in higher reliability and reduction of cost for the master controller.
However such a system must trade-off for lower performance with lower synchronicity between multiple axes for coordinated motion and lower control of drive motor behaviour. Additionally, communications between the master controller and it's plurality of connected slave units are primitive. This then results in the limitation that arises from not having the capability to fine tune or implement application specific control algorithms and the granularity of the system is thus coarser than other topologies.
Further still another system proposed by prior art is distributed control. The master controller is now realized as a form of networked device that can communicate with intelligent drives via some form of standardized communication protocol such as CANOpen or EtherCat.
Furthermore, the intelligent drives communicate with the master controller by informing all relevant information that the master controller has requested for during each communication cycle, for example, position, velocity, velocity command, current, current command etc. The master controller has the option to offer supervisory control whereby informing the slave unit on how to behave and assuming that the slave unit shall be able to perform the relevant task, or by explicitly controlling the slave unit in a limited way dictated by the duration of each communication cycle.
The topology of this architecture is via a daisy chain network. The network controller will be connected to one slave drive/module and each subsequent slave drive/module will be chained or connected one after another for example; Master to Slave A, Slave A to Slave B, Slave B to Slave C and so on.
This proposition presents a solution that allows more flexibility, a higher number of axes that can be connected, and a simplified cabling layout. However this solution suffer drawbacks as a result of poor performance with respect to being able to coordinate with multiple axis due to the bottleneck from the communication cycle time which is an inherent nature of the communication protocol between master and slave unit. Additionally this communication cycle may increase with a corresponding increase in the number of slave units connected to the system.
Due to the increased complexity and intelligence of the slave unit, the additional cost involved for implementation of such a system will be compounded. It also becomes very difficult or even impossible to perform tasks that require capturing or triggering of signals from the perspective of a multi-axis operation, with reliability or accuracy high enough that would be suitable for industrial or commercial applications.
Each of these existing three topologies has its own advantages and disadvantages when factors are considered in terms of performance, simplicity, reliability, manufacturability, flexibility, safety and cost.
Still further, this has not limited the merging of core concepts of these three main paradigms into some form of hybrid architecture as seen in prior art. Of such proposed prior art, one notable hybrid is a centralized motion control using ring or daisy chain topology as seen in the SyngNet architecture.
The position and velocity control is performed by the central controller while the current control is handled by its slave drives. At the same time, the central controller is also a networked device sending information of the current command to the slave nodes via digital information and feedback information about position and velocity is communicated back to the central controller in the same way from the slave drive.
The resulting topology borrows the very fast response of the centralized motion control topology, allowing for very high synchronicity between a plurality of drives and at the same time the complexity of wires is significantly reduced as the feedback of the drives in terms of position, velocity, input/outputs are sent in the form of digital communication as compared with a plurality of cables.
However this system must trade off with significantly increased difficulty and obstacles to implementing a robust and reliable system due to intrinsic complexity of achieving synchronicity between all drives when there is severe dependency between each drive because each is connected to each other in a daisy chain manner.
In view of the foregoing, the object of the proposed invention is to provide improved methods and apparatus for the arrangement of topology, and the communications between a centralized master unit and its' remotely distributed slave peripherals. The suggested solution retains all of the advantages of the existing methods, and eliminates most of their disadvantages, resulting with higher performance, higher reliability and lower production cost.